The present invention relates to chemical detection, and more particularly, to devices that enable analysis of compounds by high field asymmetric waveform ion mobility.
Spectrometers are used in chemical analysis for identification of compounds in a sample. These systems may take samples directly from the environment, or they may incorporate a front end device to separate or prepare compounds before analysis and detection. In some cases a quick indication of presence of particular compounds in a sample is needed, while at other times the goal is complete identification of all compounds in a chemical mixture.
The mass spectrometer is generally considered one of the most accurate detectors for compound identification. Mass spectrometers are expensive, easily exceeding $100K, and are difficult to deploy in the field. Mass spectrometers also suffer from the need to operate at low pressures, resulting in complex systems; mass spectrometers often require a highly trained operator and tend to require frequent maintenance. This presents a need for low cost, high quality, and compact chemical instruments that are capable of making a wide range of chemical identifications, as an alternative to a mass spectrometer.
There are several species of ion mobility spectrometer, all of which distinguish between chemical compounds based on ion mobility techniques. In a high field asymmetric waveform ion mobility spectrometer (FAIMS), ion filtering is achieved based on accentuating differences in mobility of ions of compounds being identified. The asymmetric field between the filter electrodes alternates between a high and low field strength that causes the ions to separate according to their mobility. Typically ion mobility in the high field differs from that in the low field. That mobility difference produces a net displacement of the ions as they travel in the gas flow through the flter. This results over time in a trajectory which, in absence of a compensation bias, causes the ions to hit one of the filter electrodes and to be neutralized. In the presence of a specific compensation bias, a particular ion species will be returned toward the center of the flow path and will pass through the filter without neutralization.
The amount of change in mobility between high field and low field and the amount of change in trajectory is compound-dependent. This permits separation of ions from each other according to their species by applying appropriately compensated filter drive signals.
In a typical FAIMS device, a gas sample, composed of a carrier gas and chemical compounds to be analyzed, is subjected to an ionization source and this ionized sample is carried by the carrier gas flow between the FAIMS filter electrodes. Application to the filter electrodes of a known asymmetric periodic voltage along with a known compensation bias, generates strong electric fields between the filter electrodes with the intent that selected ion species having a specific mobility in these known compensated high fields will flow through the FAIMS filter, if present in the sample, and these passed ions can then be detected and identified based on historical data for the device and with knowledge of the applied felds.
A planar FAIMS spectrometer with electrodes disposed over an essentially planar flow path has been disclosed which achieves a longitudinal flow and filtering of ions according to mobility differences. As well, a cylindrical FAIMS device with coaxial electrodes for longitudinal flow and filtering of ions according to mobility differences is disclosed in U.S. Pat. No. 5,420,424.
While the foregoing arrangements are adequate for a number of applications, it is still desirable to have a low cost and compact spectrometer that can render real-time or near real-time detection of chemical compounds, whether for the laboratory, the battlefield or in other environments, and whether as a stand alone detector or in cooperation with other devices such as a GC or an MS. It is also desirable to have a low-profile and portable spectrometer.
Furthermore, it is also desirable to have real-time or near real-time indication of compounds. This is important where fast indication is required to cooperate with fast sample input to the spectrometer, or possibly because of the dangers that arise from delay in detection of dangerous compounds in the environment. It is also desirable that the foregoing be achievable at low cost.
It is therefore an object of the present invention to provide a functional, small, low-cost spectrometer.
It is therefore an object of the present invention to provide a spectrometer with multiple flow paths that cooperate for fast and accurate sample processing and identification.
It is another object of the present invention to provide a chemical sensor that features the benefits of FAIMS and is able to operate rapidly, affording real-time or near real-time detection.
It is a further object of the present invention to provide a chemical sensor that features the benefits of FAIMS and can complete spectral scan in less than one second.
It is a further object of the present invention to provide a chemical sensor that features the benefits of FAIMS and is able to detect multiple ion species simultaneously.